Add fallback type (#40)

This PR adds a fallback for unsupported types.

If the column with this type is scanned from (postgres -> DuckDB) we'll
throw an error.
This makes projection pushdown work even when the table contains
unsupported columns as long as they aren't referenced.

This does not add support for the other way around, if a DuckDB type is
produced that does not have a corresponding Postgres type, this PR does
not address that issue.

.github/workflows/build_and_test.yaml

@@ -40,7 +40,7 @@ jobs:
           git clone --branch ${{ matrix.version }} --single-branch --depth 1 https://github.com/postgres/postgres.git
           pushd postgres
           git branch
-          ./configure --prefix=$PWD/inst/ --enable-cassert --enable-debug --with-openssl
+          ./configure --prefix=$PWD/inst/ --enable-cassert --enable-debug --with-openssl --with-icu --with-libxml
           make -j8 install
 
       - name: Build and test pg_quack extension

src/quack_duckdb_connection.cpp

@@ -1,5 +1,6 @@
 #include "duckdb.hpp"
 #include "duckdb/parser/parsed_data/create_table_function_info.hpp"
+#include "duckdb/main/extension_util.hpp"
 
 #include "quack/quack_duckdb_connection.hpp"
 #include "quack/quack_heap_scan.hpp"
@@ -26,6 +27,7 @@ quack_create_duckdb_connection(List *tables, List *neededColumns, const char *qu
 	    duckdb::make_uniq_base<duckdb::ReplacementScanData, quack::PostgresHeapReplacementScanData>(
 	        tables, neededColumns, query));
 
+
 	auto connection = duckdb::make_uniq<duckdb::Connection>(*db);
 
 	// Add the postgres_scan inserted by the replacement scan
@@ -35,6 +37,8 @@ quack_create_duckdb_connection(List *tables, List *neededColumns, const char *qu
 
 	auto &catalog = duckdb::Catalog::GetSystemCatalog(context);
 	context.transaction.BeginTransaction();
+	auto &instance = *db->instance;
+	duckdb::ExtensionUtil::RegisterType(instance, "UnsupportedPostgresType", duckdb::LogicalTypeId::VARCHAR);
 	catalog.CreateTableFunction(context, &heap_scan_info);
 	context.transaction.Commit();
 

src/quack_planner.cpp

@@ -40,24 +40,25 @@ quack_create_plan(Query *parse, const char *query) {
 		auto &column = preparedResultTypes[i];
 		Oid postgresColumnOid = quack::GetPostgresDuckDBType(column);
 
-		if (OidIsValid(postgresColumnOid)) {
-			HeapTuple tp;
-			Form_pg_type typtup;
+		if (!OidIsValid(postgresColumnOid)) {
+			elog(ERROR, "Could not convert DuckDB to Postgres type, likely because the postgres->duckdb conversion was not supported");
+		}
+		HeapTuple tp;
+		Form_pg_type typtup;
 
-			tp = SearchSysCache1(TYPEOID, ObjectIdGetDatum(postgresColumnOid));
-			if (!HeapTupleIsValid(tp))
-				elog(ERROR, "cache lookup failed for type %u", postgresColumnOid);
+		tp = SearchSysCache1(TYPEOID, ObjectIdGetDatum(postgresColumnOid));
+		if (!HeapTupleIsValid(tp))
+			elog(ERROR, "cache lookup failed for type %u", postgresColumnOid);
 
-			typtup = (Form_pg_type)GETSTRUCT(tp);
+		typtup = (Form_pg_type)GETSTRUCT(tp);
 
-			Var *var = makeVar(INDEX_VAR, i + 1, postgresColumnOid, typtup->typtypmod, typtup->typcollation, 0);
+		Var *var = makeVar(INDEX_VAR, i + 1, postgresColumnOid, typtup->typtypmod, typtup->typcollation, 0);
 
-			quackNode->custom_scan_tlist =
-			    lappend(quackNode->custom_scan_tlist,
-			            makeTargetEntry((Expr *)var, i + 1, (char *)preparedQuery->GetNames()[i].c_str(), false));
+		quackNode->custom_scan_tlist =
+			lappend(quackNode->custom_scan_tlist,
+					makeTargetEntry((Expr *)var, i + 1, (char *)preparedQuery->GetNames()[i].c_str(), false));
 
-			ReleaseSysCache(tp);
-		}
+		ReleaseSysCache(tp);
 	}
 
 	quackNode->custom_private = list_make2(duckdbConnection.release(), preparedQuery.release());

src/quack_types.cpp

@@ -509,7 +509,7 @@ ConvertPostgresToDuckColumnType(Form_pg_attribute &attribute) {
 		return duck_type;
 	}
 	default:
-		elog(ERROR, "(DuckDB/ConvertPostgresToDuckColumnType) Unsupported quack type: %d", type);
+		return duckdb::LogicalType::USER("UnsupportedPostgresType");
 	}
 }
 
@@ -568,8 +568,7 @@ GetPostgresDuckDBType(duckdb::LogicalType type) {
 		}
 	}
 	default: {
-		elog(ERROR, "(DuckDB/GetPostgresDuckDBType) Unsupported quack type: %s", type.ToString().c_str());
-		break;
+		return InvalidOid;
 	}
 	}
 }

test/regression/expected/projection_pushdown_unsupported_type.out

@@ -0,0 +1,18 @@
+-- XML is not supported, pushdown should avoid problems
+CREATE TABLE my_table(a TEXT, b XML, c INTEGER);
+INSERT INTO my_table (a, b, c) SELECT * from (
+	VALUES
+		('a', '<root><element>value</element></root>'::XML, 42),
+		(NULL, NULL, NULL),
+		('b', '<root><element>value</element></root>'::XML, -128),
+		('c', '<root><element>value</element></root>'::XML, 2000000)
+) t(a);
+SELECT a, c FROM my_table;
+ a |    c    
+---+---------
+ a |      42
+   |        
+ b |    -128
+ c | 2000000
+(4 rows)
+

test/regression/schedule

@@ -3,3 +3,4 @@ test: search_path
 test: execution_error
 test: type_support
 test: array_type_support
+test: projection_pushdown_unsupported_type

test/regression/sql/projection_pushdown_unsupported_type.sql

@@ -0,0 +1,10 @@
+-- XML is not supported, pushdown should avoid problems
+CREATE TABLE my_table(a TEXT, b XML, c INTEGER);
+INSERT INTO my_table (a, b, c) SELECT * from (
+	VALUES
+		('a', '<root><element>value</element></root>'::XML, 42),
+		(NULL, NULL, NULL),
+		('b', '<root><element>value</element></root>'::XML, -128),
+		('c', '<root><element>value</element></root>'::XML, 2000000)
+) t(a);
+SELECT a, c FROM my_table;